Peripheral Component Interconnect Express (PCIe) is an industry standard computer expansion technology developed by the PCI Special Interest Group (PCI-SIG). PCIe was initially designed as a local bus interconnect technology for connecting the CPU, GPU, and I/O devices in a machine, and then developed to become a completely mature switched network featuring point-to-point links, hop-by-hop flow control, end-to-end retransmission, and so on. PCIe may also be used as an expansion interface for connecting the machine and an external apparatus (e.g. a storage device).
A PCIe network is a switched network with serial point-to-point full duplex lanes. A PCIe device is connected to the PCIe network through a link formed by one or more lanes. Recently, expanded PCIe which uses a PCIe interface to interconnect multiple servers or virtualized I/O devices has become the standard. For example, application of PCIe may be further expanded to intra-rack interconnect. A PCIe switch may replace a standard top of rack (TOR) Ethernet switch. That is, PCIe may connect multiple hosts (e.g. servers) in one rack. The I/O devices that are allowed to be connected to the PCIe switch may be shared by all the servers in the same rack. All the servers in the rack may also communicate with each other through PCIe links.
Currently, the PCIe can conduct a packet transmission among multiple servers in the same rack but cannot conduct the packet transmission across different racks. Moreover, an Ethernet broadcast behavior is not supported either.